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Carbon dioxide removal on the Shuttle is performed either by flowing cabin ventilation air through single use LiOH beds or by using the Regenerable CO2 Removal System (RCRS) (Ref 1,2,3). The RCRS was designed for single string mechanical operation with redundancy only on electrical components. It therefore can become disabled by a number of possible single point failures such as fan failure, actuator failure or a large internal leak through the beds. Because of these possible failures, LiOH must be flown on all RCRS missions to provide contingency CO2 removal. These LiOH canisters occupy valuable stowage space onboard the shuttle orbiter.

The development of a new sorbent material called HS-X with significantly more CO2 removal capacity per unit volume has made much smaller sorbent bed sizes possible. With significantly smaller beds each of the single point failures can be addressed and a fully redundant RCRS can be built to fit within the existing RCRS envelope.

This paper describes the results of the design and development effort underway, as part of NASA's Orbiter Upgrade Program to make an Upgraded RCRS. The upgraded RCRS must fit within the existing RCRS envelope, match all existing plumbing, structural, and electrical interfaces, and provide both the primary and backup “CO2 removal functions. Two different approaches can meet these requirements. In this paper the two design concepts are presented and the development program is discussed.